The autonomic nervous system regulates cardiovascular functions via sympathetic outflow from preganglionic neurons in thoracolumbar spinal cord to postganglionic paravertebral and prevertebral ganglia and chromaffin cells in the adrenal medulla. Since clinical, pharmacological and neurophysiological studies suggest peptidergic influences on autonomic functions the proposed morphological studies are designed to examine the general overall hypothesis: Peptidergic containing cells and fibers located in the intermediate zone of thoracolumbar spinal cord influence the sympathetic efferent outflow controlling circulation. These studies will answer the question of whether peptidergig interactions exist within anatomically defined subunits of the sympathetic nervous system responsible for controlling cardiovascular functions? More specifically: 1) Does the segmental and nuclear immunocytochemical distribution of the peptides, enkephalin, somatostatin, and substance P differ in those areas of the intermediate zone of thoracolumbar spinal cord containing preganglionic neurons destined to innervate the superior cervical ganglia, stellate ganglia and adrenal medulla? 2) Is the origin of a peptidergic influence on autonomic functions supraspinal or intraspinal? Spinal cord transections, hemisections, dorsal and ventral rhizotomies, and specific stereotaxically placed lesions will be performed to answer this question. 3) Are these interactions between the peptides, enkephalin, somatostatin, and substance P within interneuronal and preganglionic cell populations in sympathetic nuclear regions. The technique used to resolve this question will be dual staining immunocytochemistry. 4) Do preganglionic sympathetic neurons projecting to the superior cervical ganglia, stellate ganglia and adrenal gland contain peptides and/or do the identified preganglionic neurons receive a peptidergic terminal influence. A combined retrograde transport-immunocytochemical technique will be employed to answer these questions.